In the printing industry, the inclusion of a computer-to-plate (CTP) system in a printing operation suggests a great extent of automation. A full CTP process can automate, through the use of computers and special equipment, the transfer of information from the original layout to the press plate. A computer-to-plate (CTP) system accepts input jobs/pages written in a page description language, for example, Postscript, and the jobs are sent through a raster image processor to a platemaker for exposure. The platemaker engine images the raster data on a plate, which is later mounted on a press, inked and made ready for printing.
Also included in the automation of a CTP system is the media handling. It is necessary to supply plates individually from a plate supply area to the platemaker engine and it is desirable to reduce the amount of operator handling involved. Unexposed plates are normally supplied in packages of 10 to 100 plates, with interleaf paper-sheets between the plates for protecting the emulsion side of the plates, which is extremely sensitive to scratches. The stack of plates is loaded into a supply area of a platemaker in a manner that keeps the stack of plates aligned with automation mechanisms for removing a plate from the stack, and for discarding the interleaf sheets from the stack.
While smaller plates can be loaded by hand, the advent of large printing plates has necessitated the automatic loading of plates onto the sheet materials drum or imaging drum of the CTP platesetter apparatus. While medium-sized platemaking machines with imaging drums of a few feet in length are common-place and printing plates are comparatively easy to load onto or unload from such machines, the same cannot be said for larger machines. The printing industry requires placement of plates with great accuracy when moving over distances of a meter or more. Under pressure from the printing industry for ever greater throughput, the latest generation of extra large format platemaking machines being developed at this time has imaging drums of more than 3 meters in length. At the same time there is no quarter to be sacrificed in quality and precision. It is therefore necessary to be able to load and unload extremely large and heavy materials sheets of the order of 3.15×1.60 meters in size automatically with great accuracy and precision.
One of the proven ways of securing a printing plate for imaging to an imaging drum is to employ spring loaded clamps to clamp the leading edge of the plate to the drum, to then wrap the plate around the drum and to then secure the trailing edge of the plate. In view of the larger and heavier plates being employed, one of the mechanisms developed to automatically open the clamps is to have a push rod, movably attached to a backbone that typically runs the length of the drum, that is moved down towards the clamp to push upon it in such a way as to compress the spring providing the clamping force, thereby opening the clamp and allowing the edge of the plate to be removed from the clamp.
While this was a relatively simple matter in the case of smaller machines, it becomes a rather more complex matter in systems with long imaging drums. In such large systems the sheer length of the backbone carrying the push rods, together with the greater pushing forces required to release large heavy plates from more substantial clamps, can cause the very backbone itself to flex in reaction. This complicates the loading and unloading of the printing plate involved. The same challenge translates to the presses used for printing with such large plates. Both kinds of machines have a drum, the platemaking machine and imaging drum and the press having a drum for mounting the plate imaged by a platemaking machine.
Thus, there remains a need for a simple, flexible and efficient method to load very large printing plates automatically with accuracy and precision onto a sheet materials drum for imaging, and to unload the imaged plates from the drum.